What happens in the equine foot during a laminitic attack?

Laminitic attacks are usually sudden and, unfortunately, often severe. Initially the hoof itself can form an effective visual barrier, which belies the drastic changes that take place within the foot. The pedal bone (known as P3) sits inside the hoof capsule. In a healthy foot, the outside of P3 is joined to the inside of the outer hoof wall by the interdigitating (interlocking) horny and sensitive laminae.

Laminitic foot.

The primary horny and sensitive laminae are like two packs of playing cards slotted perfectly together. They are further strengthened by the secondary laminae, which covers each primary laminal leaf to forge a massively strong attachment, fixing P3 to the outer hoof wall, and so supporting it within the foot. It is this attachment which breaks down during a laminitic attack, as the laminae bond starts to ‘unglue’ and come apart. If the horn quality is good, the attack is minor and treatment is immediate, the prognosis may be fairly good.

X-ray showing capsular rotation.

However, as the sensitive laminae start to ‘let go’ there is less support for P3 and it becomes more and more unstable. If it is only the toe area that is affected but the hoof wall remains attached at the sides, these attachments form pivot points from which P3 and descending body weight, can begin to angle downwards i.e. rotation of the pedal bone. At this time the deep digital flexor tendon can enter the picture. It attaches to the base of P3 to provide movement of the foot. As P3 becomes less anchored the force exerted by the deep digital flexor tendon has less to counteract it so P3 pivots even further downwards. Should the sensitive laminae let go completely there is nothing supporting P3, so it could penetrate through the sole of the foot, with the horse physically stepping out of its own foot. Instant euthanasia is usually the only option in this case.